The present invention relates generally to a treatment apparatus and method for hot phosphoric acid (H3PO4) solution, and more particularly, to an apparatus and method for controlling boiling conditions of hot H3PO4 solution by adjusting extracting rate thereof.
H3PO4 has a lot of applications in industries, for example, in manufacturing processes of integrated circuits formed within semiconductor substrates. It is always the case to make micro patterns on wafers in the manufacture of the integrated circuits, in which etching technique is the primary method for forming these patterns. The etching process transfers the micro pattern of a photo resist precisely rendered with lithography technique, in the form of lines, surfaces, or holes, to the material under the photo resist in order to form a complex structure required by the integrated circuit. The pattern transfer combining the etching process and lithography technique therefore plays a vital role in the semiconductor manufacturing processes.
Silicon nitride (Si3N4) is often used as a mask for forming field oxide (FOX) during oxidation processes and passivation layer over a semiconductor device. Traditionally, Si3N4 is etched by use of a spiking hot H3PO4 solution. To maximize the etching rate, deionized (DI) water spiking for the hot H3PO4 solution should be controlled and heat is provided by a heater so as to keep the H3PO4 solution in a specific boiling condition. The boiling condition of the hot H3PO4 solution can be fine-tuned, which is done by checking whether or not the temperature of the hot H3PO4 solution reaches the setting value and also by checking the boiling condition with visual inspection. In the etching process with the hot H3PO4 solution, if the boiling condition is too violent, the wafer under etched will have undesired displacement; while if the boiling condition is insufficient, an ideal etching rate will not be obtained.
However, in the practical etching processes, even though the H3PO4 solution temperature is kept constant, the DI water spiking is kept constant, and the output of the heater is also kept constant, the boiling condition of the H3PO4 solution differs. That is, the H3PO4 treatment cannot get the desired control, thus resulting in defects and loss of control in the manufacturing process. Therefore, it is desired an improved apparatus and method for a better control of boiling conditions of the H3PO4 solution.
An object of the present invention is to provide an apparatus and method for controlling boiling conditions of hot H3PO4 solution to solve the problem mentioned above.
According to the present invention, an apparatus for controlling boiling conditions of hot H3PO4 solution comprise an acid tank filled with hot H3PO4 solution thereof and located in a treatment room. A temperature thermocouple is arranged above the level surface of the hot H3PO4 solution to monitor the vapor temperature of the hot H3PO4 solution, and a damper under control is connected to the outlet of the treatment room so as to control the extracting rate of vapor from the treatment room.
According to the method of the present invention, the vapor temperature measured by the temperature thermocouple above the level surface of the hot H3PO4 solution is used to determine the boiling condition of the hot H3PO4 solution, which is in turn used to adjust the extracting rate of vapor from the treatment room in order to maintain the desired boiling condition. Given the same heating condition and the temperature of the hot H3PO4 solution being maintained constant, when the extracting rate is low, less heat is lost and the rate of heat diffusion is low, so that the hot H3PO4 solution is in a violent boiling condition. On the contrary, when the extracting rate is higher, more heat is lost and the rate of heat diffusion is high, so that the H3PO4 solution is in a gentle boiling condition.